1. Field of the Invention
This invention relates to spacecraft platforms.
2. Description of the Prior Art
Referring to FIG. 1a, part of a known satellite is shown in simplified form. The satellite has a synthetic aperture radar (SAR) antenna 1, and the associated electronics are contained in payload module 2, which supports the antenna 1 by means of struts 4. Also connected to the payload module 2 is a service module 3, containing, principally, a power supply, fuel and thrusters for adjusting the attitude and/or altitude of satellite, telemetry equipment and attitude and orbit control systems (AOCS). A solar array is also provided but has not been shown in FIGS. 1a, 1b. FIG. 1b shows in simplified form the satellite of FIG. 1a inside a fairing 5 when stowed for launch. The payload would be mounted at the top of a suitable launch vehicle (not shown). It will be seen that the antenna is stowed by being folded into four sections above the payload module 2.
One of the areas which requires a complex design solution is the SAR antenna itself. The hinges between the sections of the antenna and the associated drive mechanisms to achieve deployment are obviously critical components, and a considerable amount of design effort is required to be put into the thermo-elastic analysis of the structure to assess the range of possible distortions that may occur in a wide range of in-orbit scenarios. Even testing of the antenna on Earth is a problem, because the deployed antenna may not be self-supporting on Earth, and complicated and expensive support structures are required in view of this. Yet another problem may arise from the vibrations during launch because it is relatively difficult to tether the stowed antenna 1 to the payload module beneath.
Structurally, the payload module 2 and the service module 3 essentially consist of a box-like structure formed by the outer walls of the modules shown. In other known satellites, the modules are structurally based on a cylinder running the height or part of the height of the modules, and the outer panels are supported by radial extensions from this cylinder.
Another variant, the Milstar satellite, shown schematically in FIGS. 2a and 2b retains the service module 3 of the conventional construction of FIGS. 1a and 1b, but splits the payload module into two box-like sections 2a, 2b. These are hinged by hinges 39, 40 to the top of the service module (i.e. part way along the length of the spacecraft) and deployed as shown in FIG. 2b.
Non-payload components, such as solar panels, have been folded upright in a zig-zag shape for launch, and have been unfolded for deployment (EP-A-0 064 917). Further, it has been proposed (U.S. Pat. No. 4,964,597) to carry collapsible living quarters as a payload, of cylindrical form, which unhinges for deployment about an axis parallel to the launch axis, to produce living quarters based on two half cylindrical shells side by side.